Electrostatic printing tube and method for manufacture



March 15, 1960 w, cR ws 2,928,973

0 PRINTING TUBE AND METHOD FOR MANUFACTURE ELECTROSTATI 1 Filed 00-12. 21, 1957 2 Sheets-Sheet 1 VidO e M mm; fiz :F 08 0 a V, a M m (z. a S v M om P m a m 1% WW m, m Q A 56M V A Dielecirz'c SWEEP //5 INVENTOR. Q0berz 'ZZJ. Crews AMPLIFIER I CIRCUIT V1050 AMPL lF/FR a w h w c m N bian? FLY-"c; 2-

March 15, 1960 R. W'CREWS H 2,928,973

ELECTROSTATIC PRINTING TUBE AND METHOD EOR MANUFACTURE Filed 001:. 21, 1957 2 Sheets-Sheet 2 54/6'0 1 26 514 f fi 55 INVENTOR. Faber ll]. Crews diiomezis v is thereafter uniformly charged.

. Electrons 'which flow from ELECTROSTATIC PRINTING TUBE AND METHOD FOR MANUFACTURE Robert W. Crews, Palo Alto, Calif., assignor to A. .3. Dick Company, Niles, Ill., a corporation of Illinois Application October 21, 1957, Serial No. 691,326 2 Claims. (Cl. 313-89) powder whose grams carry charges of the opposite sign. The powder will cling to the charged areas of the paper as distinguished from the uncharged areas, making the latent charge image visible. The powder can then be permanently incorporated onto the paper in the imaged areas as by fusion, pressure, or other means.

A number of difierent systems have been proposed for applying the electrostatic chargeto the paper. In one such system, a metal plate is coated with selenium and Selenium, being a photo-conductor, drains off the surface charge in those areas which are exposed to light. There remains a charge pattern corresponding to the optical image which can thereafter be dusted with a charged powder. The resulting powder image is transferred to paper as in offset printing. The foregoing process is presently defined as the Xerox process. As an alternative to the above, the paper itself can be coated withthe photo-conductor thereby to enable elimination of'the foregoing transfer step. Still another electrostatic charge technique come prises one wherein the charge is deposited directly, on paper from the ends of a linear array of wires. The voltage on each wire is controlled by a separate electronic switch. Paper is drawn by the linear array of wires in a direction perpendicular to the array and charge patterns are formedon the paper by pulsing the voltageon the Wires in the proper sequence. While these systems profrom i In a copending application of John L. Tregay, Serial No. 658,275, filed May 10, 1957, description is made of an improved electrostatic printing system wherein use is made of a new and novel cathode-ray tube which forms the subject matter of this invention. The tube has a target wherein there are insulatingly supported a plurality of wires spaced from one another and extending through the face of the tube in a manner to provide a column of wire. points on the outside thereof. A conductor, or ground plane, extends adjacent the column of wire points in spaced relation therefrom to permit the insertion therebetween of paper or other dielectric Writing media. The conductor is coupledto the electron-beam- 'generating means in acathode ray tube in a manner so that the cathode of the, tube is at one level of the power supply voltage and the conductor is at ground level. the cathode of the tube are made to impinge upon the portion of the wire which is within the tube. The potential of that wire is thereby increased toward cathode potential until a discharge ocis required for electrostatic printing United States att 2 curs between the wire point in the face of the tube and the spaced conductor. If paper is inserted therebetween, the discharge will pass to the paper thereby leaving an electrostatic charge substantially of the same diameter as the wire point on said paper.

By passing the paper transversely to the column of wire points and by selectively applying the cathode-ray beam to the wires connected to these points which are within the cathode-ray tube, it is possible to deposit a pattern of electrostatic charges on the paper having a desired letter, number or other configuration. Means are subsequently provided to develop the electrostatic charge by dusting the paper with a dielectric-powder that clings to the charged areas as distinguished from the uncharged areas. The powder isthen permanently fixed to the paper as by heat, pressure, or other suitable means.

In the operation of the tube for printing copy, an original document is scanned, either by a mechanical scanner or by a television type camera. Sweep, intensity, and vertical scan-speed signals are derived therefrom which may be used to control the electrostatic printing tube to produce copy substantially as fast as the scanning process can be carried out. The paper which passes between the column of wire points is synchronized to move with the same speed as the vertical scanning speed. The

sweep signals are employed to control the cathode-ray beam deflection rate as it repetitively sweeps across the wires within the cathode-ray beam tube. The intensity signals are used to control the intensity of the cathoderay beam within the tube. Thus, the electrostatic writing can be elfectuated to duplicate the original.

it is an object of this invention to produce and to provide a method of producing a new and improved electrostatic printing tube of the type which may be employed in the described printing process.

More specifically, it is an object of this invention to provide a method and means, for mounting the spaced apart linear array of electrostatic conducting wires in sealed relation in the face of the tube with portions thereof extending into the tube for receiving the cathode ray beam directed thereon.

These and other objects and advantages of this inven tion will hereinafter appear and for purposes ofillustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which- Fig. 1 is a schematic diagram of an arrangement for practicing electrostatic wrig in accordance with the previously described invention;

Fig. 2 is a cross-sectional view of an electrostatic printing tube prepared in accordance with the practice of this invention;

Fig. 3 is a cross-sectional view of an electrostatic printing tube embodying the features of this invention;

Figs. 4a, 4b and 4c are sectional views illustrating how the target wires are assembled in the face of a tube in accordance with the practice of thisinvention, and

Figs. 5a, 5b and 5c are sectional views illustrating a y modification in the target assembly.

Reference is now made to Fig. l of the drawings which schematically illustrates an electrostatic printing system which makes use of the tube embodying the features of this invention. An original document 10 may be viewed by a suitable mechanical or television scanner or camera 12.- The scanning occurs not in the television manner, as by alternative lines, but by successive lines. The output of the television camera will be synchronizing signals and video signals which represent the information on the document. video signals and applies them to the control grid of the electrostatic printing tube 16, to control the intensity of the cathode-ray beam which is generated therein. Hori- A video amplifier 14 magnifies the 'a'deposit of electrostatic charges static developing and fixing apparatus 25,

'tube is sealed ofi by a "the original document being scanned. A dielectric writing medium 22, such as paper, isadvanced across the face of the tube at a rate which is determined by the rate of vertical scan of the original document 10. The paper may be advanced past the face of the tube by a pair of rollers 22a driven, as bya motor 23. The motor 23 is controlled by the output of av vertical sync amplifier 24. The input to this amplifier is the vertical sync signals of the scanner 12. For, mechanical scanners, the same motor which moves, the "document being scanned in what corresponds to a vertical direction may be employed to cflfect movement of the paper. These techniques are well known in the art of facsimile ,reproduction,.for

example, and therefore will not be: described in greater 'detail. he paperat the fac'ehof'rthe, tube.16 receives in a dot pattern which correspondsto what is seen on the original document.

known electro and then re ing tube, the paper is passed through well moved for subsequent utilization.

Fig. 2 shows in section the novel electrostatic printing tube embodying features of this invention. The tube is a cathode-ray device having a conventional electron gun 30, including a cathode 29, positioned at one end of the tube envelope 32. A focus coil 33 focuses the electron beam on the target. The video amplifier 14 applies the electron-beam control signals in a well known manner to the control grid 31 of the tube to control the intensity of the cathode-ray beam. The sweep-circuit amplifier output is applied to the conventional deflection coils 34 for the purpose of deflecting the electron-beam along the array of individual wires 36 which are mounted in the target in the face of the tube. The face of the face plate 38 made of metal, such for example as aluminum. This face plate has a slot therein in which is supported the plurality of wires 36 in a manner so that they are insulated from one another.

A source of operating potential 39 is provided for the tube, the most negative voltage being applied to the cathode and the most positive voltage being applied or connected to the ground. Also connected to ground is the face plate of the tube and a conducting rod or ground plane 40 which extends along the column of wires 36. "Thus, there is provided a coupling between the ground plane and cathode through the source of operating potential. The paper 22 passes between the conductor 45? and either brushes against the array of wires or is preferably spaced away from the wires by approximately 0.0005 of an inch. The reason that it is preferred to space the paper from the wire tips is that when the system is in operation, the paper is pulled past these wire tips at high speed and it is desired to prevent the paper from becoming charged by friction against the face plate.

Fig. 3 is a, plan view of the electrostatic printing tube target. It shows the metal face plate 38 which has therein a slot wherein is mounted a plurality of wires 36 in a manner to be insulated from one another. The points of the wires extend through the face plate. These are arranged in a column and preferably as many of these wires may be provided as are required to print a line of characters which are being scanned on the original document.

' Various techniques have been investigated for the manufacture of'the target'in the electrostatic printing tube with the wires extending throughto the face of the tube and in sealing relation therein and'wherein the wires are arranged in the desired linear array with an accurately controlled spaced relationship between the wires. The. latter two features represent characteristics which are important to the production of copy of good quality from the printing device, yet achievement of these character istics in a tube has presented numerous problems, especially in the handling of wires of such small dimension.

in accordance with the practice of this invention, a construction having the desired characteristics can be achieved in a rather simple and efficient manner. As illustrated in Figs. 4a, 4b and 40, two glass rods 40, 42 are clamped together, as in a lathe. A fine tungsten wire 44 is wound around both rods with the desired pitch for imparting the predetermined spaced, relationship between the wires. The wire which was employed in an embodiment of the invention had a diameter of 0.001 inch and was spaced apart about 1.31 times the diameter. One turn was allowed on the glass rods for each wire point desired in the finished cathode-ray tube.

As shown in Fig. 4b, two additional glass rods 46 and 48 are ground as shown and glass rod 46 has its flat side applied to the glass rod 42 toclarnp therebetween the wire turns. Glass rod 48 has its flattened side applied to bothrods 40 and 42 and it also clamps the wire between itself and the two rods. Sealing means is applied to maintain the rods in their clamped relation.

The excess glass is ground off along the dotted lines shown in Fig. 4b, leaving the portion shown as in Fig. 40. A surface 50, which is the printing surface, is obtained with points of the Wire 44 extending between the remains of glass rod 46 and glass rod 42. The grinding away of glass rod 48 and the edges of glass rod 42 on the other side of the wire is such as to leave the wire ends below the printing surface 50. These ends are masked off when the entire assembly is sealed into a slotin the face plate of the tube, which may bemade of aluminum. The electron-beam strikes the wires as indicated by the heavy arrow in Fig. 4c.

The sealing means employed to effect the desired sealing relation between the described elements includes the use of an epoxy type resinous material which can be applied as a compound of fluid consistency and advanced to a cured stage while the elements are held together to effect a sealing relationship therebetween. Advancement of the resinous material may be achieved either by heat or by catalyst or combinations of both. While a satisfactory seal can be secured by the use of a heat curable resinous material, it is preferred to make use of a glass seal wherein glass frit in the form of small beads of lower melting point glass are introduced into the space and heated to fusion to-effect the desired bonding and sealing relation. 1

A similar techniqueis. em lo yed in the system illustratedin Figs. 5a, 5b and 5c. The fine wire 44 is wound at the desired pitch for providing the desired spaced relationship about a glass rod v50 .having a rectangular shape in cross-section, such as a A x h inch rod. Another rectangular section 52 of glass, which may be of similar dimension, is joined in edge to edge relation with the rod 50 to clamp the wires 44a in sealing relationship therebetween. The joined rods are then cut or otherwise ground down along the dotted lines 54, 56 and 58 in Fig. 5b to cut off a section 60 across the frontface and another section 62 across the free edge of the rod 50 and still another section 64 forming a portion of the rear face of the rod 50. This leaves the wires in the desired spaced relation extending through the thickness of the joined rods to the front face of the target with the points of the wires in the desired spaced relation and it leaves a short tail portion 66. extending laterally in corresponding spaced relationfor a short distance across the face of the rod 50 and in position to receive the cathode-ray-beam for build-up of the electrostatic charge to be transmitted through the tube.

The assembly is then sealed into the slot in the face plate 38 ofthe tube, preferably by the use of glass frit or other suitable sealing means.

The mechanism by which a charge is deposited on the isolated from ground and ground.

tric medium. Since glass-rod portion abutting said first paper is as follows: In view of the previously described wire assembly technique, every one of the wires 44 is from each'other. Any wire upon which the ca'thode-ray-beam falls begins to charge towards cathode potential. When the potential of the wire reaches a critical value with respect to the ground plane, a discharge takes place between the wire and If a dielectric writing medium is located between the wire and the conducting rod, then a spot charge will be developed under the .wire on the dielecpaper moves at a "very high speed, best results have been obtained when the side of the the paper which is adjacent the ground conductor is somewhat conductive, although this characteristic is not essential for good results. This minimizes the development of electrostatic charges arising as a result of friction by the paper against the payout and takeup reels and other guide mechanisms.

It will be understood that sealing meansaother than those described may be employed for carrying out the desired invention and that use may be made of wires of a'diflierent dimension and of diiferent spaced relationships therebetween, depending upon the quality of copy.

that is desired. I

It will be further understood that changes may be made in the details of construction and composition without departing from the spirit of the invention especially as defined in the following" claims.

I claim: 5 1 r v V 1. In anelectrostatic printing tube an improved target comprising a metal faceplate having a slotted opening, an array filling said slotted opening, sa id array including a first glass rod, a plurality of wires each of which has a bend therein conforming to the periphery of said first glass, rod, 'said'plurality of wires being spaced along said first glass rod with their bent portions in contact therewith, a second and a third glass rod portion positioned on either side of one end of each of said plurality of wires with said one ends therebetween, said second glass rod, the sides of said second and third glass-rod portions which are adjacent the ends of said wires and which are positioned to be external to said tube forming a common plane external to said tube and exposing the ends of. said plurality of wires, a fourth glass-rod portion, said fourth glassrod portion being positioned adjacent said first glass-rod and second glass-rod portions such that said wires are positioned between it and said first glass-rod and second glass-rod portions, and bonding means between all said glass rods and plurality of wires for providing a unitary array.

2. An electrostatic printing device comprising a tube envelope having at one end a target, said target including a conductive metal faceplate having a slotted opening therein, an array filling said slotted opening, said array including a firstglass rod, a plurality of wires each of which has a bend therein conforming to the periphery of said first glass rod, said plurality of wires being spaced along said first glass rod with their ben't sportions in contact therewith, a second tion positioned on either side and a third glass-rod porof one end of each of said plurailty of wires with said one ends therebetween, said plane external to said tube and exposing the ends of' said plurality of wires, a fourth glass-rod portion, said fourthglass-rod portion being positioned adjacent said first glass-rod and second glass-rod portions such that said wiresare positioned between it and said first glassrod and second glass-rod portions bonding means between all said glass rods and plurality of wires for providing a unitary array, means for generating an electron beam at the other end of said tube envelope, means for modulating the intensity of said beam, means for defleeting said beam along said wires, a conductor positioned adjacent the ends of said plurality of wires, and means for coupling said conductor to said means for generating an electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 

